Electron discharge device



Oct. 18, 1949. w. c. BRowN 2,485,084

ELECTRON DISCHARGE DEVICE Filed April 11, 1945 2 SheetS-Sheet l Oct. 1s,1949.

w. c. BROWN ELECTRO DISCHARGE DEVICE 2 Sheets-Sheet 2 Filed April 11,1945 Patented Oct. 18, 1949 UNITED STATES PATENT OFFICE ELECTRONDISCHARGE DEVICE Application April 11, 1945, Serial No. 587,725

(Cl. Z50-27.5)

4 Claims.

This invention relates to electron-discharge devices of the typeintended to amplify or generate ultra-high frequency oscillations. Theinvention is particularly applicable to magnetrons, or otherelectron-discharge devices of the type having a plurality of cavityresonators all of which are intended to oscillate at the same frequencyand jointly contribute to the output of the device.

It is among the objects of the present invention to provide anelectron-discharge device of the type described which may be tunedthrough a wide range of frequencies.

Devices of the type to which the invention relates include an anodestructure of highly conductive material, such as copper, comprising acylindrical body having a plurality of interiorlyextending arms orvanes. Each pair of adjacent arms together with that portion of thecylindrical body lying therebetween constitute a resonant cavity. Theresonant cavities being of the same geometry are intended to oscillateat the same frequency. Since other oscillatory circuits exist in thetube other than the circuit defined by the cavities, such other circuitsmay result in oscillations at other than the desired output frequency ofthe device. In order to limit such spurious oscillations, strappingmeans may be provided adjacent the interior ends of the anode armsinterconnecting alternate of said arms. In my copending application,Serial No. 583,624, filed March 19, 1945, I have disclosed a means fortuning such devices by varying the capacitance provided by adjacentstraps.

It is among the objects of the present invention to improve devices ofthe type described and provide a construction which permits lesscritical mechanical tolerances, to provide a still wider tuning range,and to provide a construction permitting the coupling of eitherinductance or capacitance into the circuits provided by the resonantcavities.

The above and other objects and features of the invention will be madefully apparent to those skilled in the art from a consideration of thefollowing detailed description taken in conjunction with theaccompanying drawing in which:

Fig. 1 is a longitudinal section through a magnetron constructed inaccordance with the present invention; and

Fig. 2 shows a transverse section taken on the line 2 2 of Fig. 1.

Referring to the drawing, reference numeral 4 indicates anelectron-discharge device, in this instance of the magnetron type,comprising a tubular body 5 of a highly conductive material, such ascopper. The tubular body 5 is provided with a central annular projection6 from the interior surface of which a plurality of anode arms or vanes1 and 8 of copper or other conductive material project radially inregularly spaced relation to points adjacent a central cathode structure9. The cathode structure 9 comprises a sleeve IIJ conventionally ofnickel. The sleeve Il! is provided with projecting flanges II, oneadjacent the upper interior end of the anode arms 'I and 8 and the otheradjacent the lower end of said arms. The intervening portion coextensivewith the arms 1 and 8 is coated in a known manner with anelectron-emissive material. In order to support the cathode sleeve I0 inproper spaced relation with the anode arms 1 and 8, the sleeve I8 isprovided with a reduced portion I2 at the lower end thereof adapted tobe received in the upper end of an elongated tubular conductor I3. Theconductor I3 extends through a central bore I4 through a pole piece I5,and is supported in spaced relation to and concentric with said bore bymeans of a cup-shaped member I6 having an opening in the bottom portionthereof through which the tubular member I3 extends and to which it ishermetically sealed. The other end of the cup-shaped member I6 is sealedto the lower end of a glass tube I1 the opposite end of which tube issealed to a sleeve I8 of Kovar or other material readily fusible toglass. The other end of the sleeve I8 is hermetically sealed in anenlargement of the bore I4. A conductor I9 extending through the tubularsleeve I3 is supported in spaced relation thereto by means of a glassbead 20 within the tube I3 and a glass seal ZI hermetically closing theouter end of said tube. The upper end of the conductor I9 is welded to aconductor 22 leading to a heating filament 23 in the tube I0 andcoextensive with the activated surface thereof. The upper end of theheating lament 23 is connected by Wire 24 to the upper end of the nickelsleeve I0. From the foregoing it will be seen that the conductor I9constitutes one of the lead-in conductors for supplying heating currentto the coil 23 and supplying a biasing potential to the cathodestructure 9. The other connection for the heating current is effectedthrough the tubular conductor I3, the outer end of which projects beyondthe cupshaped member I6 and is connected to the other terminal of thesource of heating and biasing potential. It will also be seen that thecathode structure is insulated from the anode, externally by the glasssleeve I1 and internally by the spacing between the cathode structureand adjacent metallic structure of the anode.

The pole piece l5 is provided with a shouldered portion at which it issealed through an opening in an end cap 26 closing the lower end of thetubular body 5. The opposite end of the tubular body 5 is likewiseclosed by an end cap 27, hermetically sealed thereto and having acentral opening 28 therein. A pole piece 29 is sealed in the opening 28at a shouldered portion thereof.

Each of the anode vanes 'l is provided with a notch 30 adjacent theinner end thereof and each of the vanes 8, one of which intervenesbetween successive arms 1, is provided with a similar notch 3l of thesame dimensions as the notch 30 but positioned closer to the inner endsof the arms. A pair of concentric sleeves 3-2 and 33 mounted in the polepiece 29 project downwardly into the notches 33 and 3l. One of thesleeves, in this instance 32, is positioned to contact each of the arms'l along one edge of the notch 30 and is soldered thereto at this point.The sleeve 32 passesr freely through the notches 3| in the interveningvanes 8 without contacting said vanes. The other of the concentricsleeves 33 passes freely through the notches 30 in the vanes 'l withoutcontacting said vanes and contacts each of the vanes 8 at the outer edgeof the notches 3|. The two sleeves 32 and 33provide a section of aconcentric line, the inner conductor 32 of which is connected to thevanes 'l and the outer conductor 33 of which is connected to theintervening vanes 8. Thus the two sleeves, in addition to the functionof limiting spurious oscillations in the manner of known strappingmeans, also provide a concentric line circuit connected in parallel withthe resonant circuits with each of the resonant cavities. In order tovary the parameters of the parallel circuit so formed I provide anannular piston 34 of conductive material adjustable in the annular spacebetween the two sleeves 32 and 33. In order to vary the position of theannular piston 34 the pole piece 29 is provided with a central bore 35coaxial with the cathode structure 3. Within the' bore 35 a plunger 36having a recess 31 in the lower end thereof lto permit the same to clearthe upper end of the cathode structure `il has its upper end facesoldered to the lower face of a Sylphon bellows 38. The bellows 33 isprovided with an outwardly extending flange 39 at its upper end, whichflange is soldered upon a shoulder provided by an enlarged portion ofthe bore 35 thereby hermetically sealing said bore. An adjusting rod 40is connected to the upper interior face of the bellows 38 and extendsupwardly through the bore 35. A micrometer screw 4l on the projectingend of the rod 40 permits longitudinal adjustment of the rod by means ofa nut 42 connected to a knurled plate 42. The reciprocatory movements ofthe plunger 36 are transmitted to the annular piston 34 by means of aplurality of radially-extending arms 43 connecting said piston andplunger. The arms 43 project inwardly from the annular piston 34 throughslots 44 in the material of the pole piece 23 adjacent the lower end ofthe bore 35 and through slots 45 in the inner ring 32 to connect withthe plunger 36.

In order to limit radiation outwardly over the face of the pole piece29'1 provide an annular slot 43 in the face of this pole piece. Thisslot has a depth corresponding to approximately onequarter of the lengthof the wave generated by the tube and functions as a wave trap.

The length of the sleeves 32 and 33 is such that the annular piston 34may be adjusted so that the distance between thev upper edge of theanode arms 'l and 8 and the lower face of the piston when in itsoutermost position will be substantially greater than one-quarter of thelength of the wave generated by the tube. That portion of the sleeves 32and 33 below the upper edge of the arms 'I and 8 may be considered asintroducing additional capacitance in parallel with the oscillatorycircuit provided by the resonant cavities and functions as knownstrapping means interconnecting alternate arms to reduce or suppressspurious oscillations. That portion of the sleeve 32 and 33 above theupper edges of plates 'l and 8 and below the lower face of piston 34 maybe considered'a'sa variable length of coaxial line and introduces animpedance dependent upon the effective length of the line, which lengthmay be varied by adjustment of the annular piston 34. If the piston beso adjusted that the distance between the lower face thereof and theupper edge of the arms 'l and 8, which distance is designated as :cinthe accompanying drawing, is equal to one-quarter of the length of thewaves generated by the device, then the impedance becomes infinite. Ifthe piston 34 is adjusted so that' the distance is less than one-quarterof the length of the waves generated by the system, then the effect ofthe line is to add inductance. If the piston is so adjusted that thedistance :c is greater than one-quarter of the length of the wavesgenerated by the system, then the line adds capacitance. By adding orsubtracting capacitance or inductance, the resonant frequency may bevaried over wide limits. The frequency of operation f when the effectivelength of the coaxial line is less than may be plotted from thefollowing formula:

Cf=tube capacity,

Zo=characteristic impedance of the coaxial line,

C=velocity of light,

=length of coaxial line to lower face of piston 34.

The frequency of operation where the effective length coaxial line isgreater than may be determined by the following formula:

There has been herein described a preferred embodiment of the invention.Other embodiments within the scope of the following claims will beapparent to those skilled in the art from a consideration of the formshown and the teachings thereof.

What is claimed is :l

1. A tunable electrondischarge device comprsing an anode structureprovided with a plurality of anode members; each pair of adjacent anodemembers, together with that portion of said 'anode structure lyingtherebetween, constituting a cavity resonator; each anode member havinga slot formed therein; a pair of 'conductors disposed in said slots andalternately contacting successive anode members; said conductorsproviding a transmission line having impedance; and means on said linefor altering the effective length thereof from values greater thanone-quarter of the length of the waves corresponding to the naturalfrequencies of said cavity resonators to values less than one-quarter ofthe length of said waves.

2. A tunable electron-discharge device comprising: a cathode; an anodestructure provided with a plurality of anode members spaced from saidcathode; each pair of adjacent anode members, together with that portionof said anode structure lying therebetween, constituting ya cavityresonator; each anode member having a slot therein; a pair `ofconductive sleeves extending into said slots fand alternately contactingsuccessive anode members; said sleeves providing a coaxial transmissionline coupled to said cavity resonators; and means movable intermediatesaid sleeves for altering the eiective electrical length of saidtransmission line.

3. A tunable electron-discharge device comprising: la cathode; an anodestructure provided with a plurality of anode members spaced :from saidcathode; each pair of adjacent anode members, together with that portionof said anode structure lying therebetween, constituting a'cavityresonator; each anode member having a slot therein; a pair of spaced,concentrically disposed, conduotive sleeves extending into said slot-sand alternately contacting successive anode members; said sleevesproviding ia coaxial transmission line coupled :to said cavityresonators; and an annular piston slidably contacting the facingsurfaces of said sleeves for altering the effective electrical length ofsaid transmission line.

4. A tunable electron discharge device comprising: an anode structureincorporating a cavity resonator; a pole piece carried by said anodestructure and provided with -acentral bore, an `annular recesssurrounding said bore, and 1a slotted wall intermediate said bore andrecess; a pair of annular conductors alternately contacting successiveanode members and extending into the annular recess of said pole piece;one of said conductors being provided with slots in register with theslots in said Wall of said pole piece; a :third con-ductor mounted forreciprocation intermediate said pair of conductors; a plunger mountedfor reciprocation in the central bore of said `pole piece; and aplurality of arms connecting said 1plunger and s-aid third conductorthrough the registering slots in said Wall of said pole piece and saidyone of said conductors.

WILLIAM C. BROWN.

REFERENCES CITED The following references are of record in the le ofthis patent:

UNITED STATES PATENTS Number Name Date 2,167,201 Dallenbach July 25,1939 2,252,118 Dallenbach et al. Aug. 12, 1941 2,329,778 Nergaard Sept.21, 1943 2,414,084 Bowen Jan. 14, 1947 2,414,085 Hartman Jan. 14, 1947

